Patent GB-1404491-A (GB)
Title: Method and apparatus for making helical flutes
IPC: B24B3/04
Filed: 1972-07-21
Abstract: 1404491 Grinding helical flutes K P STANABACK 21 July 1972 34304/72 Heading B3D A method of machining helical flutes in a conical workpiece, such as a tapered end mill W, comprises orienting the workpiece with its axis generally tangential to the periphery of a rotary tool 44, such as a grinding wheel, advancing the workpiece along its axis relative to the tool with the smaller end leading while rotating the workpiece about its axis to form a helical flute, withdrawing the workpiece from the tool, rotating the workpiece through a predetermined angle before advancing the workpiece for a second time, repeating the latter three steps a number of times, periodically dressing the tool thereby decreasing its diameter, and after each dressing operation modifying the positional relationship of the tool and workpiece by an amount to accommodate for the smaller diameter of the tool. In apparatus for carrying out the method, the grinding wheel 44 is mounted on a spindle 42 driven by a motor in a housing 40 on a mount 46 vertically adjustable relative to a base 50 by a handwheel 56 or pawl-and-ratchet mechanism 58, 60 driven by a fluid cylinder 62. The grinding wheel is arranged so that its axis is at an angle to the direction of movement of a bed 14 on a base 12. A bar 70 extends from a platen 48 of the mount 46 and is secured to a reference bar 72 from which depends a vertical tapered stop 74. The stop is vertically adjustable with the grinding wheel and co-operates with an adjustable stop 76 on the bed 14. A carriage 24 has a main platform 21 which is generally L-shaped and slidable on guide rods 17, 19 mounted in blocks 13, 15 on the bed 14. Pillars 23 extend upwardly from the platform and receive pivot pins 27 mounting a support 138 for a shaft 31 which, at one end, has a chuck 140 for the workpiece, and at the other end, an indexing device 137 which has removable pins 37 co-operable with a stop 39. A belt 132 connects the device 137 to a shaft 112 connected by gearing 108, 110 to a motor 102. The shaft 112 is supported in one arm 114<SP>1</SP> of a U -shaped bracket 114, the other arm 114<SP>11</SP> of which is adjustable relative to arm 114<SP>1</SP> by a threaded member 120 to vary the backlash between a male member 116 driven by shaft 112 and a female member 118 connected to a chuck 144. A shaft 146 of a cam 148 having a helical cam track 151 is mounted in chuck 144, the track being engaged by followers (153, Fig. 16, not shown) on a sleeve 150 carried by a bracket 152 on a carriage 154 slidable along guide rods 156 supported by blocks 158, 160 on the bed 14. The carriage 154 is connected by a pivot pin 182 to a dogleg link 180, one end of which is mounted on a pivot 184 on the bed 14, and the other end of which has a block 190 slidable in a track 192 of a member 194 adjustable about a pivot 206 to positions determined by engagement of a pin 200 with selected holes 202 in a sine plate 198. A rod 214 extends transversely across the bed 14 and at one end is connected by links 210, 212 to the sine plate 198, and at the other end is fixed to a link 216 having a follower 218 engaging the bar 22 whereby vertical adjustment of the grinding wheel acts, through the rod 214 and dogleg link 180, to move the carriage 154 a distance corresponding to the vertical movement and hence the reduction in size of the grinding wheel following dressing by a tip 240 carried by a dog 242 movable about a pin 244 on the bed by a nose 250 on a sine bar 252 on the platform 21 as the latter is moved past the grinding wheel. The forward and return movements of the platform are controlled by limit switches actuated by adjustable dogs on a rod 311 secured to the carriage 154 so that the limits of the to-and-fro movement of the platform is also adjusted in response to the reduction in size of the grinding. The vertical adjustment also causes the vertical tapered stop 74 to vary the position of the bed 14 at the start of each grinding operation to accommodate change in size of the wheel. The support 138 for the chuck holding the workpiece is adjustable about the pins 27 by engagement of a stop with a bar 252 secured to the support to adjust the axis of the workpiece so that it is inclined to the horizontal at, for example, half the angle of the taper of the workpiece. The end mill is tapered and may have three cutting edges 408<SP>111</SP>, Fig. 11, which are formed during forward movement of the end mill by the grinding wheel machining the flutes 406 and cutting face 408<SP>1</SP>. During the return stroke, the backlash between the members 116, 118 causes the wheel to grind the relief surfaces 410 upon reverse rotation of the motor 102 driving the cam and end mill. The relief surface may extend to the cutting edge or leave an arcuate surface 408, which surface may be ground flat during subsequent sharpening operations.